The present invention relates generally to implantable, radially expandable medical prostheses which are frequently referred to as stents. In particular, the present invention is a bioabsorbable self-expanding stent.
Self-expanding medical prostheses frequently referred to as stents are well known and commercially available. They are; for example, disclosed generally in the Wallsten U.S. Pat. No. 4,655,771, the Wallsten et al. U.S. Pat. No. 5,061,275 and in Hachtmann et al., U.S. Pat. No. 5,645,559. Devices are used within body vessels of humans for a variety of medical applications. Examples include intravascular stents for treating stenoses, stents for maintaining openings in the urinary, biliary, tracheobronchial, esophageal, and renal tracts, and vena cava filters.
A delivery device which retains the stent in its compressed state is used to deliver the stent to a treatment site through vessels in the body. The flexible nature and reduced radius of the compressed stent enables it to be delivered through relatively small and curved vessels. In percutaneous transluminal angioplasty, an implantable endoprosthesis is introduced through a small percutaneous puncture site, airway, or port and is passed through various body vessels to the treatment site. After the stent is positioned at the treatment site, the delivery device is actuated to release the stent, thereby allowing the stent to self-expand within the body vessel. The delivery device is then detached from the stent and removed from the patient. The stent remains in the vessel at the treatment site as an implant.
Stents must exhibit a relatively high degree of biocompatibility since they are implanted in the body. An endoprosthesis may be delivered into a body lumen on or within a surgical delivery system such as delivery devices shown in U.S. Pat. Nos. 4,954,126 and 5,026,377. Preferred delivery devices for the present invention include U.S. Pat. Nos. 4,954,126; 5,026,377. Suitable materials for use with such delivery devices are described in U.S. patent application Ser. No. 08/833,639, filed Apr. 8, 1997.
Commonly used materials for known stent filaments include Elgiloy® and Phynox® metal spring alloys. Other metallic materials than can be used for self-expanding stent filaments are 316 stainless steel, MP35N alloy, and superelastic Nitinol nickel-titanium. Another self-expanding stent, available from Schneider (USA) Inc. of Minneapolis, Minn., has a radiopaque clad composite structure such as shown in U.S. Pat. No. 5,630,840 to Mayer. Self-expanding stents can be made of a Titanium Alloy as described in U.S. patent application Ser. No. 08/598,751, filed Feb. 8, 1996.
The strength and modulus of elasticity of the filaments forming the stents are also important characteristics. Elgiloy®, Phynox®, MP35N and stainless steel are all high strength and high modulus metals. Nitinol has relatively low strength and modulus.
The implantation of an intraluminal stent will preferably cause a generally reduced amount of acute and chronic trauma to the luminal wall while performing its function. A stent that applies a gentle radial force against the wall and that is compliant and flexible with lumen movements is preferred for use in diseased, weakened, or brittle lumens. The stent will preferably be capable of withstanding radially occlusive pressure from tumors, plaque, and luminal recoil and remodeling.
There remains a continuing need for self-expanding stents with particular characteristics for use in various medical indications. Stents are needed for implantation in an ever growing list of vessels in the body. Different physiological environments are encountered and it is recognized that there is no universally acceptable set of stent characteristics.
A need exists for a stent which has self expanding characteristics, but which is bioabsorbable. A surgical implant such as a stent endoprosthesis must be made of a non-toxic, biocompatible material in order to minimize the foreign-body response of the host tissue. The implant must also have sufficient structural strength, biostability, size, and durability to withstand the conditions and confinement in a body lumen.
All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties for all purposes.